Fighting Sathanas is more about endurance than it is about rushing him down. The map itself hints at this by encouraging the player to grind mdef to avoid the curse while also allowing you to set up shortcuts so you have more time remaining before you get cursed.

While I'm not sure if bloodshot eyes can be taken in conjunction with lascivious coating, anti-magic coating + lascivious coating + bloodshot should push your slime somewhere north of 80 mdef. Considering that hi-Sathanas has an effective matk of 25 before day 100 on normal mode, a few blessed apples should suffice to get your slime to tank another hit or two. And once Hi-demon Sathanas is out of mana, your slime has done its duty and should probably die to avoid giving Sathanas free tactical advantage(shifting to into wind slime at that point might work if fly lets you dodge dark basic attacks but again, haven't tested that one).

But when I said blessed bombs, that included blessed acid bombs. Hi-Sathanas with broken defenses before day 100 effectively has the same amount of def/mdef as a regular scorpio. Just keep cycling light II and regular attacks and heal Aura when needed and you should be able to get through his 18k health in 18-24 turns.

...come to think of it, It's possible that you're supposed to use radiance instead of water skin and hope the combination of distraction slime, tactical advantage and/or blessed vitality potions can get Aura past past the fire spells in good enough health for the slugfest that follows.